As related hearing aids, the one is the behind-the-ear (BTE) hearing aids and the other is the in-the-ear (ITE) hearing aid. The ITE hearing aid includes a completely-in-the-canal hearing aid, a concha-type hearing aid and a canal-type hearing aid. Recently hearing aid users tend to prefer a BTE hearing aid to an ITE type, because the BTE hearing aid is compact and unobtrusive when the user put it on a behind a pinna.
Some example, related-art behind-the-ear hearing aids have two constituent elements. The two constituent elements are a behind-the-ear (Behind The Ear: BTE) section and a completely-in-the-canal (Completely In the Canal: CIC) section. The BTE is equipped with a microphone, a battery, and signal processing unit; and a receiver is provided in an ear canal. Hitherto, a sound has been transmitted from a hearing aid main unit to an eardrum by way of an acoustic guide tube. The hearing aid yields an advantage of the ability to transmit sounds in wide frequency bands directly to an eardrum by way of placing a receiver in an ear canal (see; for instance, Patent Document 1). The receiver to be placed in the ear canal is referred to as a receiver in a canal (Receiver in Canal: RIC).
Another behind-the-ear hearing aid enables easy and specific adjustment for individual differences, such as the shape and size of a pinna of a hearing aid wearer. As shown in FIG. 8, the hearing aid is made up of an ear fitting 800 to be disposed in a dent in a pinna and a behind-the-ear portion 810. The ear fitting 800 has a microphone 801 and a receiver 803, and the behind-the-ear portion 810 has a signal processing section 802 and a power source. In this hearing aid, the length of the ear fitting 800 is adjustable in an extensible manner with respect to the behind-the-ear portion 810, and an angle of the ear fitting is adjustable in a rotatable manner (see; for instance, Patent Document 2).